Single crystals of ${\mathrm{EuAu}}_2{\mathrm{In}}_4$ containing divalent ${\mathrm{Eu}}^{2+}$ ions with spin-only large angular momentum $S=7/2$ have been successfully grown. A comprehensive study reveals that this compound undergoes two successive antiferromagnetic transitions at $T_{N1}=8.7\mathrm{K}$ and $T_{N2}=6.9\mathrm{K}$. An application of external magnetic field suppresses both phase transitions, driving the system to a potential field-induced antiferromagnetic quantum critical point. Although ${\mathrm{EuAu}}_2{\mathrm{In}}_4$ behaves as a large-local-moment antiferromagnet lacking significant Kondo coupling, pronounced spin fluctuations involving electronic degrees of freedom emerge over an extended region near the putative quantum critical point, as evidenced by $T$-quasilinear resistivity and enhanced specific-heat coefficient. Related to the unexpected quantum critical behaviors, we identify a characteristic temperature line $T^{*}\left(B\right)$ traversing the antiferromagnetic phase in the temperature-field phase diagram. This energy scale is associated with a Zeeman-like splitting of the $S=7/2$ multiplet in the strong internal exchange field. The resulting spin-state distribution gives rise to an extended low-temperature regime characterized by effectively reduced spin momentum, which might play an essential role in determining the quantum critical behaviors.

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• Kondo effect
• Quantum phase transitions
• DC susceptibility measurements
• Magnetization measurements
• Resistivity measurements
• Specific heat measurements